The present invention relates to catalysts and processes for the photochemical decarboxylation of alpha-hydroxy carboxylic acids to selectively form the corresponding alcohols.
The realization that petroleum feedstocks are limited, nonrenewable resources has stirred interest in the production of what are considered petroleum-derived products by alternative technological means, such as the conversion of biomass to useful hydrocarbons.
As an example, there are now three commercial processes for the production of ethanol: synthesis from ethylene or formation as a by-product of n-butane oxidation, both of which are reliant on petroleum feedstocks, and fermentation of sugar-containing carbohydrates which is a time-consuming process. Currently, most U.S. production of ethanol is derived from ethylene, while internationally fermentation accounts for more than half of the ethanol production. Alternative technological means are being considered for producing alcohols such as ethanol. Alcohols may be obtainable from biomass-derived compounds such as alpha-hydroxy carboxylic acids. Such a process may utilize a photochemical reaction.
It is well known that chemical compounds may be converted into other useful chemicals by means of photo-induced reactions. Euler and Ryd reported in The Decomposition of Lactic Acid and Tannic Acid in Ultraviolet Light, Biochemische Zeitschrift, Vol. 51, pp. 97-103, 1913, that lactic acid undergoes cleavage at 70.degree. C. in the presence of ultraviolet light to form formic acid and acetaldehyde and that these products were rapidly converted to ethanol and carbon dioxide. No yields of ethanol were reported.
Photochemical processes generally utilize a catalyst in conjunction with light to obtain the desired reaction. Recently, semiconductor materials have been utilized as catalysts for selective photo-induced chemical reactions. One such semiconductor material is titanium dioxide. U.S. Pat. No. 4,303,486 to Bard et al. discloses heterogeneous photocatalytic decarboxylation of saturated carboxylic acids to form carbon dioxide and the corresponding alkanes. Bard et al. utilized titanium dioxide as the catalyst for this photo-induced reaction. The catalyst was anatase and could be doped and/or platinized. Bard et al. did not disclose product yields.
While photo-induced chemical reactions and semiconductor materials are known, the application of semiconductor materials to photo-induced chemical reactions is not well known nor is it predictable. Catalytic activity of one reaction system does not imply that similar conditions and catalysts will behave in a similar manner when applied to a different reaction.
It would be a significant advance in the field of photochemistry to provide means for producing what are considered petroleum-derived products from materials that are not petroleum-based. Specifically, it would be a technical contribution to the area of photo-induced chemical reactions to provide means for the production of alcohols from alpha-hydroxy carboxylic acids.
Thus, it is an object of this invention to provide novel catalysts for the photo-induced decarboxylation of alpha-hydroxy carboxylic acids to predominantly form the corresponding alcohols.
It is another object of this invention to provide a photochemical process for the decarboxylation of alpha-hydroxy carboxylic acids.
These and other objects of the invention will become apparent in the description of the invention and examples which follow.